From time to time my iTunes behaves very strange and restarts itself when I try to quit it. This is very annoying as one can’t even shutdown or reboot the computer in this situation as iTunes will always interupt the shutdown process. Only a hard reboot will help

I did some research and found the solution on a blog and the Apple Forum. The main cause of this behaviour is the SRS iWOW plugin. This has a process called “genredetection” which will restart iTunes if it quits unexpectedly. When iTunes restarts it will spawn a new genredetection process. Now when you try to shutdown iTunes normally then it’s OK for the new genredetection process. But not for the remainder of the last iTunes session. So it will restart iTunes. Now a new genredetection process is spawned ….

The only way to stop this is to terminate all the genredetection processes manually. You can do this via the ActivityMonitor.app or in the Terminal.app by typing killall genredetection. After this iTunes can be quitted normally.